This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPPthird generation partnership projectUTRANuniversal terrestrial radio access networkNode Bbase stationUEuser equipmentHOhandoverE-UTRANevolved UTRANaGWaccess gatewayeNBEUTRAN Node B (evolved Node B)MACmedium access controlMMmobility managementPHYphysicalRLCradio link controlRRCradio resource controlPDCPpacket data convergence protocolMMEmobility management entityO&Moperations and maintenanceLTElong term evolutionFDDfrequency division duplexOFDMAorthogonal frequency division multiple accessSC-FDMAsingle carrier, frequency division multiple accessULuplinkDLdownlinkOLPCopen loop power controlIoTinterference over thermal noiseOIoverload indicatorTPCtransmission power controlPopower output
A communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. The current working assumption is that the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
One specification of interest to this invention is 3GPP TS 36.300, V8.2.0 (2008-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8).
FIG. 1 reproduces FIG. 4 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC (Evolved Packet Core), more specifically to a MME (Mobility Management Entity) by means of a S1-MME interface and to a Serving Gateway (S-GW) by means of a S1 interface. The S1 interface supports a many to many relation between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:                functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);        IP header compression and encryption of user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        a measurement and measurement reporting configuration for mobility and scheduling.        
The OI is currently under discussion in 3GPP RAN WG1 for LTE. The basic concept as presently understood is that the eNB measures the uplink interference over thermal noise (IoT). If the IoT is above a certain threshold, then an event is triggered where an OI message is sent to the eNBs of neighboring cells. The OI may be measured across the entire system bandwidth, or it may be measured for a set of defined sub-bands covering the full system bandwidth, as proposed in R1-074042, R1-071634, and other 3GPP contributions.
Reference in this regard may be made to 3GPP TSG RAN1 #50-bis, R1-074042, Shanghai, China, Oct. 8-12, 2007, “Uplink Inter-cell Power Control: X2 Messages”, Motorola; and to 3GPP TSG RAN WG1 Meeting #48bis, R1-071634, St. Julians, Malta, Mar. 26-30, 2007, “Investigations on Inter-cell Transmission Power Control based on Overload Indicator in E-UTRA Uplink”, NTT DoCoMo.
More specifically, R1-074042 states that the contents of the X2 message for uplink inter-cell power control should include the following:
quantized IoT level per sub-band (1 or 2 bits);
the load of the cell (1 or 2 bits);
uplink performance satisfaction index (1 or 2 bits); and
other information may be included if proved to be beneficial.
The granularity of the frequency dependent IoT level is said should be configurable and allow the whole bandwidth IoT level be a special case. For example, in case of a relatively large site, the uplink is noise limited and the frequency dependent IoT report might not be necessary.
The X2 messages may be event-driven and sent no faster than every 20 ms. The events may include high/un-acceptable IoT, unsatisfactory uplink performance, and changes of the load in the cell. Due to the X2 delay (20 ms), the measurement (averaging) interval for IoT needs to be of the same order.
With regard to the usage of the overload indicator, R1-074042 states that when the eNode-B receives these X2 messages, it may perform the (inter-cell) power control adaptation schemes in the following ways:
Approach 1: Node-B adapts the parameters of power control formula and then broadcast them to the UEs;
Approach 2: Node-B adjusts the transmission power of individual UEs;
Approach 3: Node-B broadcasts the (processed) X2 messages, the UEs then adapt their transmission power accordingly.
Since the eNode-B has all the information, it is said that it would be natural to adopt Approach 1 or 2 and perform centralized adaptation without additional signaling defined. Approach 3 relies on UEs to adapt their power. After the UE adapts its transmission power, its power headroom needs to be updated to the eNode-B for scheduling or measurement/PA errors correction.
It can be noted that it is further stated that exactly how the eNode-B adapts the parameters of the power control formula, and adjusts the transmission power of UEs, may be specified in order for the inter-operation between eNode-Bs from different vendors.
The above referenced R1-071634 shows in Table 1 (reproduced herein as FIG. 2) various simulation parameters related to inter-cell TPC schemes. The parameters that were used were optimized so that the achievable cell throughput becomes the highest provided without degradation in the 5%-user throughput against the case with only intra-cell TPC. It was assumed that the transmission interval of the overload indicator is 1 msec for all approaches. In Approaches 1 and 2, the threshold of the interference-over-thermal (IoT) is set to 12-15 dB, while in Approach 3 the threshold of IoT per interfering UE is set to 6 dB. If the IoT exceeds the threshold, the overload indicator requests the UEs to decrease the transmission power by 1 dB in Approaches 1 and 3. Otherwise, the transmission power is increased by 1 dB. In Approach 2, according to the algorithm described in 3GPP, R1-063478, Lucent Technologies, “Uplink Scheduling with Inter-Cell Power Control, with Extensions to Interference Coordination”, the step size of the transmission power offset is weighted using the path loss difference between the serving cell and non-serving cell. Further, assuming that the control delay in transmission of the overload indicator is 4 ms, the UE only follows the overload indicator, which corresponds to the previous transmission of that UE. In order to avoid excessive power reduction by the overload indicator for the UE near the cell edge, it was assumed that the UE would not lower the transmission power by more than −10 dB of that determined by intra-cell TPC. It was also assumed that all UEs monitor the overload indicator from only a single neighboring cell, which has the lowest propagation loss, i.e., path loss+shadowing+penetration loss. The monitored cell is reselected every 100 ms. However, if the lowest propagation loss value exceeds the propagation loss value of the serving cell by more than 6 dB, no single neighboring cell is monitored and the transmission power is determined using intra-cell TPC.
It should be noted that, as currently considered, the OI is exchanged between eNBs, and there is no direct connection between the OI and a UE in a neighbor cell.
The UL LTE may use the OLPC according to a formula presented in 3GPP TSG-RAN WG1 #49-bis, R1-073224, Orlando, USA, Jun. 25-29, 2007, “Way Forward on Power Control of PUSCH”, CATT, Ericsson, LGE, Motorola, Nokia, Nokia-Siemens, Nortel, NTT DoCoMo, Orange, Panasonic, Philips, Qualcomm, Samsung, Sharp, TI, Vodafone.
The power control formula for the PUSCH is outlined as below:PC formula: P=min(Pmax,10 log(M+Po+α×PL+delta_mcs+f(delta—i))[dBm], whereUE obeys the power setting formulation based on the parameters signaled by the networkM is the number of assigned RBs (based on UL grant)Po is a cell specific parameter that is broadcasted (default value)a is cell specific path loss compensation factor (can be set to one to allow full path loss compensation)PL is downlink pathloss calculated in the UEdelta_mcs is signaled by RRC (table entries can be set to zero)                MCS signaled in UL grantdelta_i is UE specific correction value included in the UL grant        Function f(*) signaled via higher layers                    Only two possibilities            Accumulated vs. absolute valueThis should be consistent with interference coordination.                        
It is known that the setting of the uplink OLPC parameters determines the IoT operation point of the network. For a given path loss compensation factor (also known as Alpha), the setting of the OLPC parameter Po has a high impact on the obtained IoT. However, the mapping from Po to the actually experienced IoT depends strongly on, for example, the path-loss distribution and the cell topology. As a result, in practice it is non-trivial to set the Po parameter corresponding to the desired IoT operation point.
What is currently not resolved is exactly what action(s) that the eNB should take as a function of the OI, and exactly how the eNB should use the OI information.